1. Field of the Invention
The present invention relates to devices and related methods for determining the maximum temperature to which a temperature indicator was exposed and, more particularly, to devices and related methods wherein the temperature indicator comprises a body of polymeric material.
2. Description of Related Art
An industrial science called "Failure Analysis" has been developed over the years to determine after the fact what has caused the failure of a complex mechanical or electrical device. An important part of Failure Analysis is looking for indications of a portion of the device being exposed to temperatures that exceed its design limits. These indications can be physical and/or chemical changes in the device's materials which can be detected by smell, by microscopic analysis, by chemical analysis, by X-ray diffraction, and the like, as well as by operating temperature recordings, if available. There is a need in all of these methods for determining the exposure temperatures as quickly, as accurately, and as inexpensively as possible.
Many mechanical devices are used in environments where electromechanical temperature indicators, such as thermocouples and gauges that generate a signal representative of temperature, cannot be used due to space limitations, exposure to extreme temperatures, pressures and corrosive chemicals, and cost. For example, electromechanical temperature indicators usually cannot be used within chemical process equipment and within subterranean wellbores. So, when a failure occurs within a pump, motor, turbine, valve or drill bit used in these environments, a costly and time consuming Failure Analysis must be performed. This Failure Analysis could be performed more quickly and less expensively if some indicator could be developed and used which could remain part of the device but record the maximum temperature to which the device was exposed.
Another problem with prior electromechanical temperature indicators is that a single thermocouple can only indicate the operating temperature of a certain portion of the device adjacent which the thermocouple is located. While the portion of the device where the thermocouple may be located is operating at a temperature that is satisfactory, an adjacent portion of the device may be overheating. For example, a thermocouple can indicate that the oil or coolant temperature of an internal combustion engine is satisfactory, yet the temperature of one of the main bearings may be excessive.
Prior maximum temperature indicators included expensive and difficult to manufacture films or coatings that could be applied directly to the article to be investigated. Such prior indicators are disclosed in U.S. Pat. Nos. 3,415,122; 3,472,074; 3,839,898; and 4,272,988.
A prior maximum temperature indicator that was developed to meet some of the above described needs comprises a plurality of resin bodies which are attached on or within a device, with each such resin body being formed from a material with a different melting point. Examples of these prior indicators are disclosed in U.S. Pat. Nos. 3,802,269 and 4,390,291. When the device is exposed to a temperature that exceeds the melting points of particular bodies, upon inspection the operator can easily determine which bodies have melted and which bodies have not in order to determine the approximate maximum temperature to which the device was exposed. While these bodies provide a relatively inexpensive temperature indicator, the bodies cannot be used in devices where melted material might foul the operation of the device or undergo chemical attack, nor in very confined spaces within certain devices. Additionally, the bodies can only provide an approximation of the maximum exposure temperature, with the approximation dependant upon the number of bodies used and the difference in melting temperature of one body to the next.
There is a need for an inexpensive maximum temperature indicator which can be used in hostile environments, in confined spaces, and which can provide an indication of the exact temperature to which the device was exposed.